Chapter 1: Cells – the Basic Building Blocks of Life

Lesson 6: Understanding Diffusion Describe the process of diffusion and its relation to the cell. Plan a fair test investigation to explore the factors affecting diffusion. Explain how the different factors speed up or slow down diffusion.

Lesson 6: Chemicals on the move All cells require chemicals including glucose, oxygen, nutrients and minerals in order to survive. These pass through the cell membrane by diffusion, a process by which substances move from an area of high concentration to one of low concentration, until the concentrations are equal. There have to be more particles outside the cell than inside for them to move into the cell. Cells also produce waste products, such as carbon dioxide and urea. They move out of the cell by diffusion because there are more waste particles inside the cell compared to outside.

Lesson 6: Factors affecting diffusion TEMPERATURE: It occurs more rapidly at higher temperatures because the particles have more energy and move faster. CONCENTRAION: The number of particles in a given volume is called the concentration of a solution. In a highly concentrated solution, the nutrients diffuse faster into the cell compared to when it is in an area of low concentration. SURFACE AREA: The ratio of the surface area of the cell to its volume affects how quickly diffusion across the cell membrane can occur

Lesson 6: Effect of Surface Area How long a unicellular organism can survive depends on the rate of diffusion of chemicals into and out of a cell The ratio of surface area to volume effects how quickly diffusion will happen The higher the ratio the more quickly diffusion will take place Surface area of a cube is calculated by finding the area (A = b • h) of one side of cube and multiplying by the number of faces. (SA = 6(b•h)) Volume of a cube is calculated by multiplying the length x width x height of the cube (V = l • w • h) Ratio is found by dividing the surface area by the volume (SA ÷ V)

Lesson 6: Key Vocabulary and Notes Key Vocabulary: glucose, diffusion, surface area, volume Key Notes: Substances move from the outside to the inside of a cell by a process called diffusion Factors that effect diffusion include: temperature, concentration, ratio of surface area to volume The smaller the cell the higher the ratio of surface area to volume the faster diffusion happens

Lesson 6: Questions and Answers 1. What is the process by which substances move from higher concentration to lower concentration called? Ans. Diffusion 2. Which has a greater effect on diffusion: temperature or concentration? Ans. Temperature because the particles have more energy 3. Calculate the surface area to volume ratio for these cubes: length = 1 cm SA1 = 6(1 x 1) = 6 SA2 = 6(2 x 2) = 24 Volume = 1x 1x1 = 1 Volume = 2x2x2 = 8 Ratio = 6: 1 Ratio = 4:1